PyQCD

PyQCD is a lattice-QCD toolkit in Python with optional native acceleration. It provides building blocks for propagator and operator contractions, gradient flow, renormalisation and gluon TMD-PDF extraction, plus a self-contained contraction engine with an opt_einsum-compatible API.

Install

pip install pyqcd

The native kernels are optional: without a C++ compiler (or without CUDA) the package installs anyway and the contraction engine runs its pure-Python planner — same results, only slower.

Set PYQCD_EINSUM_REQUIRE_NATIVE=1 to make a missing toolchain a hard error.

Documentation

• English — https://py-qcd.readthedocs.io/en/latest/usage.html
• 中文 — https://py-qcd.readthedocs.io/zh-cn/latest/usage.html

Quick start

import numpy as np
import pyqcd.einsum as pe

a = np.arange(6.0).reshape(2, 3)
b = np.arange(12.0).reshape(3, 4)

pe.contract("ij,jk->ik", a, b)                       # like a @ b
path, info = pe.contract_path("ij,jk->ik", a, b)     # (path, PathInfo)
int(info.opt_cost)

expr = pe.contract_expression("ij,jk->ik", (2, 3), (3, 4))
expr(a, b)                                           # reusable plan

The public surface mirrors opt_einsum: contract, contract_path, contract_expression, shared_intermediates, PathInfo, paths, backends, helpers, parser, blas.

What is inside

Contraction engine

• Pure-Python planning (greedy / optimal / branch / dp) is always available.
• Two optional native backends: KUPL (CPU) and CUDA (GPU). Both export the same C ABI and share one planning core.
• Fallback is a hard invariant: a missing library, a failed native call or a rejected shape silently degrades to the Python path — results never change.
• A small set of lattice-QCD equation shapes gets a specialised execution path; it is enabled by default and can be turned off per call (contract(..., specialize=False)) or per process (PYQCD_EINSUM_SPECIALIZE=0).

Introspection:

import pyqcd.einsum as pe

pe.build_info()        # backend, mpi, mpi_label, native_library
pe.mpi_enabled()       # whether the KUPL library has real MPI support
pe.specializations()   # registered equation shapes

MPI sharding exists only in the KUPL backend and only shards a single output axis; the CUDA backend has no MPI implementation.

Tests

Run from a source checkout:

python -m pyqcd.testing                       # integration suite
bash pyqcd/testing/simple/run-all.sh          # per-function API parity vs opt_einsum
bash pyqcd/testing/einsum/simple/run-all.sh   # einsum sub-system suite

License

MIT